1. Field of the Invention
The present invention relates to image forming apparatuses such as copier machines, printers, facsimile machines, and multifunction apparatuses that include these, as well as fixing devices used in these image forming apparatuses.
2. Description of the Related Art
Hitherto, technologies have been proposed involving a fixing device installed in an image forming apparatus such as a copier machine and a printer or the like in which a nip portion (fixing nip portion) is formed, which transports a recording medium, by causing two roller members to press against each other, for example, in Japanese Unexamined Paten Application Publication No. 2004-333973. A fixing device such as this is constituted by components such as two roller members (a fixing roller and a pressure roller), a pressure means for causing the two roller members to press against each other, a heater that heats the fixing roller, a heating means such as an exciting coil, and a drive gear that transmits driving force by engaging with one of the two roller members. And by heating the fixing roller using the heating means, a toner image on the recording medium that has been transported to the nip portion is subjected to heat and pressure, thereby fixing it on the recording medium.
On the other hand, the technologies disclosed in Japanese Unexamined Paten Application Publication No. 2004-333973 involve using helical gears and using gears that transfer thrust in the drive gear train, which transmits driving force to the fixing device, for a purpose of carrying out drive transmission to the fixing roller in such a manner that speed fluctuations and noise tend not to occur.
However, with the aforementioned conventional fixing device, when the two roller members are left for a long period in a state pressing against each other, sometimes permanent warping (plasticity deformation) is produced undesirably in a plane form at a position corresponding to the nip portion of the roller members. Then, when rotational drive is performed (when the apparatus is operated) in this state in which permanent warping has been produced in the roller member, the rotation velocity of the roller member sometimes momentarily increases undesirably when the position where permanent warping has been produced reaches the nip portion. In a case such as this, the drive gear installed on a shaft portion of the roller members arrives early with respect to the rotation of a gear that it meshes with (a gear on an upstream side of the drive gear) such that their tooth surfaces collide, thereby producing an undesirable collision sound.
Furthermore, the aforementioned prior art was devised for a purpose of carrying out drive transmission such that speed fluctuations and noise tend not to occur with respect to the fixing roller even when a leading edge side of the recording medium reaches the fixing nip portion and a trailing edge side of the recording medium has reached a transfer nip portion, and does not directly address the aforementioned problems.